Transport device, transfer device, and image forming apparatus

ABSTRACT

A transport device includes a transporting member that transports an object that is wound around an outer peripheral surface thereof by rotating; a holding unit that is rotatably supported by the transporting member at a first end thereof, the holding unit holding a leading end of the object in a transport direction by gripping the leading end between a second end thereof and the outer peripheral surface when the object enters a space between the second end and the outer peripheral surface; and a positioning unit disposed on the transporting member or the holding unit so as to be movable downstream in a direction in which the object enters the space. The positioning unit contacts the leading end of the object that has entered the space and positions the object in the transport direction when the holding unit moves to hold the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-049253 filed Mar. 6, 2012.

BACKGROUND Technical Field

The present invention relates to a transport device, a transfer device, and an image forming apparatus.

SUMMARY

According to an aspect of the invention, a transport device includes a transporting member that transports an object that is wound around an outer peripheral surface thereof by rotating; a holding unit that is rotatably supported by the transporting member at a first end thereof, the holding unit holding a leading end of the object in a transport direction by gripping the leading end between a second end thereof and the outer peripheral surface when the object enters a space between the second end and the outer peripheral surface; and a positioning unit disposed on the transporting member or the holding unit so as to be movable downstream in a direction in which the object enters the space. The positioning unit contacts the leading end of the object that has entered the space and positions the object in the transport direction when the holding unit moves to hold the object.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a schematic view illustrating the structure of an image forming apparatus;

FIG. 2 is a schematic view illustrating the structure of a leading end gripper;

FIG. 3 is a perspective view illustrating the structure of the leading end gripper;

FIGS. 4A and 4B illustrate the structure of the leading end gripper;

FIGS. 5A to 5D illustrate a gripping operation performed by the leading end gripper;

FIGS. 6A to 6C illustrate the gripping operation performed by the leading end gripper;

FIG. 7 is a schematic view illustrating an appropriate retracted position of a positioning unit of the leading end gripper; and

FIG. 8 is a schematic view illustrating the structure of a leading end gripper according to a comparative example.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present invention will be described with reference to the drawings. Structure of Image Forming Apparatus according to Present

Exemplary Embodiment

First, the structure of an image forming apparatus according to the present exemplary embodiment will be described. FIG. 1 is a schematic view illustrating the structure of an image forming apparatus 50 according to the present exemplary embodiment.

As illustrated in FIG. 1, the image forming apparatus 50 includes an image forming apparatus body 62 and various components disposed in the image forming apparatus body 62. An image forming unit 10, a recording medium feeder 40, and a controller 60 are disposed in the image forming apparatus body 62. The image forming unit 10 forms an image on a recording medium P, which is an example of an object. The recording medium feeder 40 feeds the recording medium P to the image forming unit 10. The controller 60 controls the operation of each component of the image forming apparatus 50. A recording medium output unit 63 is disposed on an upper part of the image forming apparatus body 62. After an image has been formed on the recording medium P by the image forming unit 10, the recording medium P is output to the recording medium output unit 63.

The recording medium feeder 40 includes a recording medium container 41 and a transport unit 45. The recording medium container 41 contains the recording medium P. The transport unit 45 transports the recording medium P from the recording medium container 41 to the image forming unit 10. The transport unit 45 includes a feed roller 42 and plural transport rollers 44. The feed roller 42 feeds the recording medium P contained in the recording medium container 41. The transport rollers 44 are arranged along a transport path 51 of the recording medium P and transport the recording medium P, which has been fed by the feed roller 42, to the image forming unit 10.

The image forming unit 10 includes a photoconductor drum 11 and a transfer device 20. The photoconductor drum 11 is an example of an image carrier that carries an image. The transfer device 20 transfers the image (toner image), which is carried by the photoconductor drum 11, to the recording medium P. The photoconductor drum 11 rotates in one direction (for example, the direction of arrow A in FIG. 1).

A charging roller 12, an exposure device 13, a rotary developing device 14, and a cleaner 15 are arranged around the photoconductor drum 11 in the rotation direction of the photoconductor drum 11. The charging roller 12, which is an example of a charger, charges the photoconductor drum 11. The exposure device 13 exposes the photoconductor drum 11, which has been charged by the charging roller 12, with light, and thereby forms an electrostatic latent image on the photoconductor drum 11. The rotary developing device 14, which is an example of a developing device, develops the electrostatic latent image, which has been formed on the photoconductor drum 11 by the exposure device 13, and thereby forms a toner image. The cleaner 15 cleans residual toner (developer) remaining on the photoconductor drum 11.

The exposure device 13 forms an electrostatic latent image on the basis of an image signal sent from the controller 60. Examples of an image signal sent from the controller 60 include an image signal received by the controller 60 from an external apparatus.

The rotary developing device 14 includes a rotation shaft 14A; and developing units 14Y, 14M, 14C, and 14K for yellow (Y), magenta (M), cyan (C), and black (K), which are arranged around the rotation shaft 14A in the circumferential direction of the rotation shaft 14A. The rotary developing device 14 rotates around the rotation shaft 14A in the direction of arrow C. When one of the developing units 14Y, 14M, 14C, and 14K of the rotary developing device 14 is located at a facing position at which the developing unit faces the photoconductor drum 11, an electrostatic latent image formed on the photoconductor drum 11 is developed by using a color toner corresponding to the developing unit located at the facing position, and thereby a toner image is formed.

The transfer device 20 includes a transfer drum 21, which is an example of a transporting member. The transfer drum transports the recording medium P, which is wound around the outer peripheral surface thereof, by rotating. In the transfer device 20, the recording medium P, which has been transported by the transport unit 45, is wound around the outer peripheral surface of the transfer drum 21 (to be specific, the outer peripheral surface of an elastic layer 21B described below), and rotates together with the photoconductor drum 11. As a result, the recording medium P is transported to a transfer position Tr (transfer region) between the transfer drum 21 and the photoconductor drum 11, and the transfer drum 21 transfers a toner image from the photoconductor drum 11 to the recording medium P. That is, the transfer drum 21 also functions as an example of a transfer member and transfers a toner image from the photoconductor drum 11 to the recording medium P. As described below, a leading end gripper 23 and a trailing end gripper 27 respectively grip the leading end and the trailing end of the recording medium P in the transport direction, and thereby the recording medium P is wound around the outer peripheral surface of the transfer drum 21.

The recording medium P is supplied to the transfer drum 21 at a supply position Pa shown in FIG. 1 (a holding-start position at which the leading end gripper 23 (described below) starts holding the recording medium P). The recording medium P is peeled off the transfer drum 21 at a peel-off position Pb (a holding-finish position at which the leading end gripper 23 finishes holding the recording medium P) shown in FIG. 1. The structure of the transfer device 20 will be described below in detail.

A fixing unit 30 is disposed downstream of (in FIG. 1, above) the transfer position Tr along the transport path 51. The fixing unit 30 fixes the toner image, which has been transferred to the recording medium P by the transfer device 20, to the recording medium P. The fixing unit 30 includes a heating roller 31 and a pressing roller 32. The heating roller 31 heats the toner image on the recording medium P. The pressing roller 32 presses the recording medium P as a result of being pressed against the heating roller 31.

In the fixing unit 30, the recording medium P is pressed and heated by the pressing roller 32 and the heating roller 31, which rotate with the recording medium P therebetween while transporting the recording medium P downstream (in FIG. 1, upward) along the transport path 51. As a result, the toner image is fixed to the recording medium P.

Output rollers 46 are disposed downstream of the fixing unit 30 along the transport path 51. The output rollers 46 output the recording medium P, to which the toner image has been fixed, to the recording medium output unit 63. Structure of Transfer Device 20 according to Present

Exemplary Embodiment

Next, the structure of the transfer device 20 according to the present exemplary embodiment will be described.

As illustrated in FIG. 1, the transfer device 20 includes the transfer drum 21, the leading end gripper 23, and the trailing end gripper 27. The leading end gripper 23, which is an example of a leading end holding member, is disposed on the transfer drum 21 and grips the leading end of the recording medium P in the transport direction. The trailing end gripper 27, which is an example of a trailing end holding member, is disposed on the transfer drum 21 and grips the trailing end of the recording medium P in the transport direction.

A detection sensor 25 for detecting passage of the recording medium P is disposed so as to face the outer peripheral surface of the transfer drum 21. The detection sensor 25 is disposed upstream of a standby position (described below) of the trailing end gripper 27 (the position of the trailing end gripper 27 shown in FIG. 1) in the transport direction of the recording medium P.

Transfer Drum 21

As illustrated in FIG. 1, the transfer drum 21 is disposed in the image forming apparatus body 62 so as to face the photoconductor drum 11 and so as to be rotatable around a rotation shaft 21D. The transfer drum 21 includes a base member 21A having a cylindrical shape and the elastic layer 21B formed on the outer peripheral surface of the base member 21A.

The base member 21A is electroconductive and is made of, for example, a metal material. The elastic layer 21B is made of a semi-conductive elastic material (for example, a resin material such as a polyurethane resin).

The transfer drum 21 rotates in the direction of arrow B in synchronism with the rotation of the photoconductor drum 11 while the elastic layer 21B is in contact with the photoconductor drum 11. A part of the elastic layer 21B that contacts the photoconductor drum 11 becomes elastically deformed.

A voltage (transfer bias) having a polarity opposite to that of toner is applied to the base member 21A of the transfer drum 21, and thereby a toner image is transferred from the photoconductor drum 11 to the recording medium P, which is wound around the elastic layer 21B, at the transfer position Tr.

A portion of the outer peripheral surface of the base member 21A in the circumferential direction is not covered with the elastic layer 21B. This portion, in which the base member 21A is exposed, will be referred to as an exposed portion 21C. Even when the exposed portion 21C faces the photoconductor drum 11, the exposed portion 21C does not contact the photoconductor drum 11.

In FIGS. 1 and 2, the outer periphery of the transfer drum 21 when the elastic layer 21B is elastically deformed is shown by two-dot chain line K. For clarity, the two-dot chain line K is drawn around the entire circumference of the transfer drum 21.

Trailing End Gripper 27

As illustrated in FIG. 1, the trailing end gripper 27 straddles the outer peripheral surface of the transfer drum 21 in the axial direction of the transfer drum 21. The trailing end gripper 27 is supported by support portions 27A disposed at ends of the transfer drum 21 in the axial direction so that the trailing end gripper 27 is capable of contacting and becoming separated from the outer peripheral surface of the transfer drum 21.

The support portions 27A are rotatably supported by a rotation shaft 27D, which is coaxial with the rotation shaft 21D of the transfer drum 21. The trailing end gripper 27 rotates around the transfer drum 21 independently of the transfer drum 21.

The trailing end gripper 27 is located at a predetermined standby position (the position of the trailing end gripper 27 shown in FIG. 1) on the outer periphery of the transfer drum 21 before gripping the recording medium P. The standby position is, for example, a position between the transfer position Tr (transfer region) and the supply position Pa in the rotation direction of the transfer drum 21.

The trailing end gripper 27 is made of a resin material (such as PET, a polyimide resin, or a fluorocarbon resin) and has a plate-like shape extending in the axial direction of the transfer drum 21. The length of the trailing end gripper 27 in the axial direction is larger than the maximum width of the recording medium P (in the axial direction of the transfer drum 21), which is wound around the transfer drum 21. Alternatively, the trailing end gripper 27 may have a wire-like shape, a solid cylindrical shape, or the like.

When the detection sensor 25 detects passage of the trailing end of the recording medium P in the transport direction, the trailing end gripper 27 moves from a position in which the trailing end gripper 27 is separated from the transfer drum 21 to a position in which the trailing end gripper 27 contacts the transfer drum 21, and thereby holds the trailing end of the recording medium P by gripping the trailing end between the trailing end gripper 27 and the outer peripheral surface of the transfer drum 21 (to be specific, the outer peripheral surface of the elastic layer 21B).

Leading End Gripper 23

As illustrated in FIG. 2, the leading end gripper 23 is disposed in the exposed portion 21C of the transfer drum 21. The leading end gripper 23 rotates together with the transfer drum 21.

The leading end gripper 23 includes a holding unit 22 and a positioning unit 24. The holding unit 22 is rotatably supported by the transfer drum 21 (to be specific, the base member 21A) at a base end of the holding unit 22. The holding unit 22 holds the leading end of the recording medium P in the transport direction by gripping the leading end between a second end of the holding unit 22 and the outer peripheral surface of the transfer drum 21. The positioning unit 24 is disposed on the transfer drum 21. The positioning unit 24 contacts the leading end of the recording medium P and positions the recording medium P in the transport direction while the recording medium P is held by the holding unit 22.

A facing member 29, which faces the holding unit 22, is disposed in the exposed portion 21C on the base member 21A of the transfer drum 21. The facing member 29 has a facing surface 29A that faces the holding unit 22. The facing surface 29A is located inside of the outer peripheral surface of the elastic layer 21B (to be specific, inside of the outer periphery (two-dot chain line K) of the elastic layer 21B in an elastically deformed state). In the present exemplary embodiment, the facing surface 29A is a part of the outer peripheral surface of the transfer drum 21, and the holding unit 22 grips the leading end of the recording medium P in the transport direction between the holding unit 22 and the facing surface 29A. Alternatively, the holding unit 22 may grip the leading end of the recording medium P in the transport direction between the holding unit 22 and the elastic layer 21B or between the holding unit 22 and the base member 21A.

The holding unit 22 has a plate-like shape extending in the axial direction of the transfer drum 21. The length of the holding unit 22 in the axial direction is larger than the maximum width of the recording medium P, which is wound around the transfer drum 21, in the axial direction of the transfer drum 21. As illustrated in FIG. 2, when seen from an end in the longitudinal direction, the holding unit 22 has a shape that is bent so as to be convex outward in the radial direction of the transfer drum 21 (diagonally toward the upper left side in FIG. 2).

As illustrated in FIG. 3, at a tip end of the holding unit 22, plural protruding portions 227 are arranged in the longitudinal direction X of the holding unit 22. The protruding portions 227 protrude upstream in the rotation direction of the transfer drum 21. The protruding portions 227 of the holding unit 22 hold the leading end of the recording medium P in the transport direction. Plural cutout portions 223, which extend from the tip end toward the base end of the holding unit 22, are formed between the protruding portions 227 so as to be arranged in the longitudinal direction X of the holding unit 22. Due to the presence of the cutout portions 223, the positioning unit 24 is movable toward the base end of the holding unit 22 (downstream in the rotation direction of the transfer drum 21).

As illustrated in FIGS. 4A and 4B, the base end of the holding unit 22 is supported by a swing shaft 22C so as to be swingable with respect to the base member 21A of the transfer drum 21. Thus, the holding unit 22 is movable between a contact position (see FIG. 4A) in which the tip end of the holding unit 22 (an upstream end in the rotation direction of the transfer drum 21) contacts the facing surface 29A of the facing member 29 and a separated position (see FIG. 4B) in which the tip end is separated from the facing surface 29A of the facing member 29.

When the holding unit 22 is located in the separated position, the holding unit 22 allows the recording medium P to enter a space S between the holding unit 22 and the facing surface 29A of the facing member 29. When the holding unit 22 is located in the contact position, the holding unit 22 is capable of holding the recording medium P, which has entered the space S, by holding the recording medium P between the holding unit 22 and the facing surface 29A of the facing member 29. That is, the contact position of the holding unit 22 is, in other words, a gripping position in which the holding unit grips the recording medium P.

When the holding unit 22 is located in the gripping position, the holding unit 22 is capable of passing the transfer position Tr without contacting the photoconductor drum 11. That is, when the holding unit 22 is located in the gripping position, the holding unit 22 is located inside of the two-dot chain line K in FIG. 2.

An attachment portion 225 is integrally formed with the base end of the holding unit 22. A tension spring 22B, which is an example of an elastic member (urging member), is attached to the attachment portion 225. The attachment portion 225 extends downward from the swing shaft 22C in FIG. 4A (toward the rotation shaft 21D of the transfer drum 21 (see FIG. 1)). The tension spring 22B pulls the attachment portion 225 with its elastic force, and thereby the holding unit 22 is urged toward the gripping position (contact position).

A cam 22D is disposed below the attachment portion 225 in FIGS. 4A and 4B (between the attachment portion 225 and the rotation shaft 21D of the transfer drum 21 (see FIG. 1)). The cam 22D functions to move the holding unit 22 to the separated position. The cam 22D is fixed to a cam shaft 26, rotates together with the cam shaft 26, contacts the attachment portion 225, and moves the holding unit 22 to the separated position against the elastic force of the tension spring 22B.

The positioning unit 24 has a plate-like shape extending in the axial direction of the transfer drum 21. The length of the positioning unit 24 in the axial direction is larger than the maximum width of the recording medium P, which is wound around the transfer drum 21, in the axial direction of the transfer drum 21. As illustrated in FIG. 4A, when seen from an end in the longitudinal direction, the positioning unit 24 has a shape that is bent so as to be concave toward the holding unit 22 (diagonally toward the upper left side in FIG. 4A).

As illustrated in FIG. 3, at a tip end of the positioning unit 24, plural protruding portions 243 are arranged in the longitudinal direction. The protruding portions 243 protrude into the cutout portions 223 of the holding unit 22. The protruding portions 243 are disposed so as to be substantially perpendicular to the holding unit 22. The protruding portions 243 are movable through the cutout portions 223 from the tip end of the holding unit 22 toward the base end of the holding unit 22. The protruding portions 243 of the positioning unit 24 contacts the leading end of the recording medium P.

As illustrated in FIGS. 4A and 4B, a base end of the positioning unit 24 (a downstream end in the rotation direction of the transfer drum 21) is supported by a swing shaft 24C so as to be swingable with respect to the transfer drum 21 (to be specific, the base member 21A). Thus, the positioning unit 24 is movable between a positioning position and a retracted position. When the holding unit 22 is located in the contact position, the positioning unit 24 is in the positioning position and positions the recording medium P in the transport direction (an entry direction (the rotation direction of the transfer drum 21)). When the holding unit 22 is located in the separated position, the positioning unit 24 is in the retracted position, in which the positioning unit 24 is retracted from the positioning position toward the base end of the holding unit 22 (the downstream end in the transport direction of the recording medium P).

As the positioning unit 24 moves from the positioning position toward the retracted position, the recording medium P is allowed to enter more deeply into the space S between the holding unit 22 and the facing surface 29A of the facing member 29.

An attachment portion 245 is integrally formed with the positioning unit 24. A tension spring 24B, which is an example of an elastic member (urging member), is attached to the attachment portion 245. The attachment portion 245 extends downward from the swing shaft 24C in FIG. 4A (toward the rotation shaft 21D of the transfer drum 21 (see FIG. 1)). The tension spring 24B pulls the attachment portion 245 with its elastic force, and thereby the positioning unit 24 is urged toward the positioning position.

A cam 24D is disposed on the left side the attachment portion 245 in FIGS. 4A and 4B (on the downstream side in the rotation direction of the transfer drum 21). The cam 24D functions to move the positioning unit 24 to the retracted position. As with the cam 22D, the cam 24D is fixed to the cam shaft 26, rotates together with the cam shaft 26, contacts the attachment portion 245, and moves the positioning unit 24 to the retracted position against the elastic force of the tension spring 24B.

Thus, the cam 24D for moving the positioning unit 24 and the cam 22D for moving the holding unit 22 are fixed to the single cam shaft 26, and the cam shaft 26 is rotated by the single drive motor 28 (driving unit), which is controlled by the controller 60. When the cam shaft 26 is rotated by the drive motor 28, the cams 24D and 22D rotate together, and the cams 24D and 22D respectively contact the attachment portion 245 of the positioning unit 24 and the attachment portion 225 of the holding unit 22.

The phase difference between the cams 24D and 22D is set so that the positioning unit 24 moves from the positioning position to the retracted position when the holding unit 22 moves toward the separated position and so that the positioning unit 24 returns to the positioning position when the holding unit 22 moves from the separated position to the contact position. Thus, the movement of the positioning unit 24 is linked to the movement of the holding unit 22. That is, the cams 24D and 22D also function as examples of a linkage unit and link the movement of the positioning unit 24 to the movement of the holding unit 22.

As heretofore described, the trailing end gripper 27 and the leading end gripper 23 respectively grip the trailing end and the leading end of the recording medium P in the transport direction, and thereby the recording medium P is wound around the outer peripheral surface of the transfer drum 21. The positioning unit 24 and the holding unit 22 are each made of a metal material such as a stainless steel (SUS).

Image Forming Operation of Image Forming Apparatus 50

Next, an image forming operation of forming a toner image on the recording medium P, which is performed by the image forming apparatus 50 according to the present exemplary embodiment, will be described.

Before an image forming operation is started, the trailing end gripper 27 is located at the standby position between the transfer position Tr and the supply position Pa in the rotation direction of the transfer drum 21.

When the image forming operation is started, the feed roller 42 feeds the recording medium P from the recording medium container 41, and the transport rollers 44 transport the recording medium P toward the transfer drum 21. While the recording medium P is transported toward the transfer drum 21, the transfer drum 21 rotates and the leading end gripper 23 moves toward the supply position Pa.

When the recording medium P has been transported to the transfer drum 21 by the transport rollers 44, the leading end gripper 23 grips the leading end of the recording medium P in the transport direction at the supply position Pa. While the transfer drum 21 rotates, the leading end of the recording medium P in the transport direction, which is gripped by the leading end gripper 23, passes through the space Sa between the transfer drum 21 and the trailing end gripper 27 located at the standby position. After the leading end of the recording medium P in the transport direction has passed through the space Sa, the trailing end gripper 27 grips the trailing end of the recording medium P in the transport direction. Thus, the leading end gripper 23 and the trailing end gripper 27 respectively grip the leading end and the trailing end of the recording medium P in the transport direction, and thereby the recording medium P is wound around the outer peripheral surface of the transfer drum 21.

The transfer drum 21 and the trailing end gripper 27 rotate in synchronism with each other while the recording medium P is wound around the outer peripheral surface of the transfer drum 21, and thereby the recording medium P is rotated. Thus, the recording medium P is transported to the transfer position Tr.

In the image forming unit 10, the photoconductor drum 11 is charged by the charging roller 12 (charging) and exposed to light by the exposure device 13 (exposure), and thereby an electrostatic latent image is formed on the photoconductor drum 11. The electrostatic latent image is developed by the developing unit 14Y that faces the photoconductor drum 11, and thereby a yellow toner image is formed on the photoconductor drum 11 (development). The yellow toner image is transferred by the transfer drum 21 to the recording medium P, which has been transported to the transfer position Tr.

The transfer drum 21 and the trailing end gripper 27 rotate in synchronism with each other, and thereby rotate the recording medium P. The rotary developing device 14 rotates to a position at which the developing unit 14M faces the photoconductor drum 11. Charging, exposure, and development are performed as described above to form a magenta toner image on the photoconductor drum 11. The magenta toner image is transferred to the recording medium P, which is transported to the transfer position Tr again while the transfer drum 21 and the trailing end gripper 27 rotate. Likewise, cyan (C) and black (K) toner images are successively transferred to the recording medium P in an overlapping manner.

After the toner images have been transferred to the recording medium P in an overlapping manner, the leading end gripper 23 releases the leading end of the recording medium P in the transport direction at the peel-off position Pb, and thereby the recording medium P is peeled off the transfer drum 21.

The recording medium P, which has been peeled off the transfer drum 21, is transported to the fixing unit 30, and the toner images are fixed to the recording medium P by the fixing unit 30. The recording medium P, on which the toner images have been fixed, is output to the recording medium output unit 63 by the output rollers 46. An image forming process is performed as heretofore described.

Function of Present Exemplary Embodiment

Next, a gripping operation performed by the leading end gripper 23 to hold the recording medium P, which is a function of the present exemplary embodiment, will be described.

As illustrated in FIG. 5A, before the gripping operation is started, the holding unit 22 is located in the contact position, in which the holding unit 22 is in contact with the facing surface 29A of the facing member 29 (that is, the gripping position, in which the holding unit 22 is to grip the recording medium P). At this time, the positioning unit 24 is located in the positioning position, in which the positioning unit 24 is to position the recording medium P in the transport direction.

When the gripping operation is started, the drive motor 28, which is controlled by the controller 60, rotates the cam shaft 26 (forward) and thereby the cams 24D and 22D rotate (forward). Then, the cams 24D and 22D respectively contact the attachment portion 245 of the positioning unit 24 and the attachment portion 225 of the holding unit 22 (see FIG. 4B).

Thus, as illustrated in FIG. 5B, the holding unit 22 starts moving from the contact position (see FIG. 5A) toward the separated position, in which the holding unit 22 is separated from the facing surface 29A of the facing member 29. At the same time, the positioning unit 24 starts moving from the positioning position toward the retracted position, in which the positioning unit 24 is retracted toward the base end of the holding unit 22.

As illustrated in FIG. 5C, when the holding unit 22 reaches the separated position, the positioning unit 24 reaches the retracted position. At this time, the angle θ1 between the holding unit 22 and an outer peripheral surface 21E of the transfer drum 21 (to be specific, the elastic layer 21B) is smaller than 90 degrees.

As illustrated in FIG. 7, the retracted position of the positioning unit 24 may be located further toward the base end of the holding unit 22 (toward the center of the transfer drum 21) from an intersection E of the holding unit 22 and the outer peripheral surface 21E of the transfer drum (to be specific, the elastic layer 21B). In this case, when the recording medium P enters the space S between the holding unit 22 and the facing surface 29A of the facing member 29, the recording medium P is more likely to first contact the holding unit 22 than the positioning unit 24.

As illustrated in FIG. 5D, the recording medium P enters the space S between the holding unit 22 and the facing surface 29A of the facing member 29 when the holding unit 22 is located in the separated position and the positioning unit 24 is located in the retracted position.

As illustrated in FIG. 6A, the leading end of the recording medium P, which has entered the space S between the holding unit 22 and the facing surface 29A of the facing member 29, first contacts the holding unit 22, because the positioning unit 24 is located in the retracted position. Then, the leading end of the recording medium P is guided along the holding unit 22 that is inclined at the angle θ1, which is relatively small, toward the base end of the holding unit 22.

Next, the drive motor 28, which is controlled by the controller 60, rotates the cam shaft 26 (backward) and thereby the cams 24D and 22D rotate together (backward). As a result, the cams 24D and 22D respectively become separated from the attachment portion 245 of the positioning unit 24 and the attachment portion 225 of the holding unit 22 (see FIG. 4A).

Thus, as illustrated in FIG. 6B, the holding unit 22 starts moving from the separated position toward the gripping position (contact position). At the same time, the positioning unit 24 starts moving from the retracted position toward the positioning position. Thus, the recording medium P is pushed back toward the tip end of the holding unit 22.

As illustrated in FIG. 6C, when the holding unit 22 reaches the contact position, the positioning unit 24 reaches the positioning position. Thus, the holding unit 22 holds the recording medium P by gripping the recording medium P between the holding unit 22 and the facing surface 29A of the facing member 29, and the positioning unit 24 positions the recording medium P in the transport direction while the recording medium P is held by the holding unit 22. The holding unit 22 holds the recording medium P at the supply position Pa illustrated in FIG. 1.

As heretofore described, with the present exemplary embodiment, because the positioning unit 24 moves to the retracted position, the recording medium P is allowed to enter more deeply into the space S between the holding unit 22 and the facing surface 29A of the facing member 29. As a result, the recording medium P is unlikely to be unintentionally removed from the holding unit 22. Therefore, with the structure according to the present exemplary embodiment, occurrence of insufficient gripping of the leading end of the recording medium P in the transport direction by the holding unit 22 is reduced as compared with a structure in which the positioning unit 24 does not move.

Since occurrence insufficient gripping of a recording medium by the holding unit 22 is reduced, displacement of a transfer position (image formation position) on a recording medium due to such insufficient gripping by the holding unit 22 is reduced.

With the present exemplary embodiment, when the recording medium P enters the space S between the holding unit 22 and the facing surface 29A of the facing member 29, the leading end of the recording medium P first contacts the holding unit 22 and then the leading end is guided along the holding unit 22. At this time, the leading end of the recording medium P is not likely to be bent, because the angle θ1 between the holding unit 22 and the outer peripheral surface 21E of the transfer drum 21 (to be specific, the elastic layer 21B) is smaller than an angle θ2 between the positioning unit 24 and the outer peripheral surface 21E of the transfer drum 21 (to be specific, the elastic layer 21B).

FIG. 8 illustrates a comparative example in which the positioning unit 24 does not retract and the leading end of the recording medium P first contacts the positioning unit 24 when the recording medium P enters the space S between the holding unit 22 and the facing surface 29A of the facing member 29. In this case, the angle θ2 is larger than 90 degrees (cf. FIG. 5C), and therefore the recording medium P rises sharply along the positioning unit 24. As a result, the leading end of the recording medium P is likely to become bent.

With the present exemplary embodiment, the positioning unit 24 returns to the positioning position when the holding unit 22 grips the recording medium P. Therefore, the holding unit 22 grips a smaller portion (area) of the recording medium P than in a case where the positioning unit 24 does not return to the positioning position. Thus, the margin of the recording medium P is reduced, and an image may be formed in a larger region.

With the present exemplary embodiment, a driving force is transmitted from the single drive motor 28 to the holding unit 22 and the positioning unit 24, and thereby the movement of the positioning unit 24 is linked to the movement of the holding unit 22. Therefore, an error in the movements of the holding unit 22 and the positioning unit 24 is smaller than in a case where the movements of the holding unit 22 and the positioning unit 24 are controlled by driving the holding unit 22 and the positioning unit 24 by using different driving units.

Modifications

In the present exemplary embodiment, the positioning unit 24 is disposed on the transfer drum 21. However, this is not necessarily the case. For example, the positioning unit 24 may be disposed on the holding unit 22.

In the present exemplary embodiment, the movement of the holding unit 22 is linked to the movement of the positioning unit 24. However, this is not necessarily the case. In the present exemplary embodiment, the holding unit 22 and the positioning unit 24 start moving at the same timing. However, they may start moving at different timings.

In the present exemplary embodiment, a driving force is transmitted from the single drive motor 28 to the positioning unit 24 and the holding unit 22 and the movement of the positioning unit 24 is linked to the movement of the holding unit 22. However, this is not necessarily the case. For example, the movement of the holding unit 22 and the movement of the positioning unit 24 may be controlled by driving the holding unit 22 and the positioning unit 24 by using different driving units.

The present invention is not limited to the exemplary embodiment described above and may be modified, changed, and improved in various ways. For example, the modifications described above may be used in combination.

The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents. 

What is claimed is:
 1. A transport device comprising: a transporting member that transports an object that is wound around an outer peripheral surface thereof by rotating; a holding unit that is rotatably supported by the transporting member at a first end thereof, the holding unit holding a leading end of the object in a transport direction by gripping the leading end between a second end thereof and the outer peripheral surface when the object enters a space between the second end and the outer peripheral surface; and a positioning unit disposed on the transporting member or the holding unit so as to be movable downstream in a direction in which the object enters the space, the positioning unit contacting the leading end of the object that has entered the space and positioning the object in the transport direction when the holding unit moves to hold the object.
 2. The transport device according to claim 1, wherein the positioning unit moves from a positioning position, in which the positioning unit positions the object, downstream in the transport direction when the holding unit moves toward a separated position in which the second end of the holding unit is separated from the outer peripheral surface, and wherein the positioning unit returns to the positioning position when the holding unit moves from the separated position to a gripping position in which the holding unit grips the leading end of the object between the second end and the outer peripheral surface.
 3. The transport device according to claim 2, further comprising: a linkage unit that transmits a driving force from a single driving unit to the holding unit and the positioning unit and that links movement of the positioning unit to movement of the holding unit.
 4. A transfer device that is the transport device according to claim 1, wherein the object is a recording medium and the transporting member is a transfer member that transfers an image received from the outside to the recording medium.
 5. An image forming apparatus comprising: the transfer device according to claim 4; and an image carrier that carries an image that is to be transferred by the transfer device.
 6. The transport device according to claim 1, wherein the holding unit interferes with the positioning unit when seen from an axial direction of the transporting member, a plurality of protruding portions are formed in the second end of the holding unit, a plurality of protruding portions are formed in an end of the positioning unit, and the protruding portions of the positioning unit are arranged between the protruding portions of the holding unit when the holding unit moves to hold the object. 